AI Agent Observability: The 4 Pillars That Keep Your Agents from Burning $2,000 at 3 AM

Last month, a production agent at a startup started hallucinating customer data. Every API call returned 200 OK. The agent's dashboard showed green across the board. Latency was normal. Error rate was zero. Six hours later, the billing arrived: $2,847 in tokens for a single user query that entered a